This invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to an improved limit stop system for defining the maximum range of motion of the actuator of a disc drive.
Disc drives of the type known as "Winchester" disc drives or hard disc drives are well known in the industry. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path.
As is well known in the industry, when power to the disc drive is lost, a voice coil actuator, such as that just described, includes no elements to maintain control of the relative position of the coil to the permanent magnets, and thus the position of the heads relative to the discs. For this reason, it is common practice in the industry to move the heads to a park position, or landing zone, and to latch the actuator there until power is restored to the disc drive.
It is also common practice in the industry to incorporate a system of limit stops in the disc drive to define the maximum range of motion of the actuator. Such limit stops are necessary to prevent damage to the heads, flexurcs or discs should the actuator attempt to move the heads into an unintended relationship with the discs due to either a loss of disc drive power or a failure in the logic controlling the actuator position.
Historically, the limit stops in a disc drive have included some sort of mechanism which provides for a selected amount of compliance when the limit stops are encountered. Such compliance is necessary to prevent damage to the delicate mechanical components of the flexures used to mount and support the heads which could be brought about by abrupt deceleration of the actuator. Various mechanisms for providing this selected compliance have been used, including springs, elastomers, dash pots and moving mass.
It has also been common practice to provide features, such as tabs or pins, on the moving portion of the actuator, and to provide separate inner and outer limit stop mechanisms against which the features of the moving portion of the actuator are brought into contact. Another typical practice is to incorporate the latching mechanism used to hold the actuator in the park position into the mechanism of the inner limit stop.
One major drawback of such separate inner and outer limit stops lies simply in the number of components that must be incorporated in the disc drive, increasing the cost of the disc drive.
Secondly, having separate inner and outer limit stops also requires that precise location mechanisms for both of these components must be provided. Indeed, in some prior art limit stop systems, both position of both the inner and outer limit stops is an adjustment that must be manually performed during the manufacturing process, again contributing to both the complexity and cost of the disc drive.
A need clearly exists, therefore, for an improved limit stop system for the actuator in a disc drive that minimizes parts count and assembly steps while still providing precise location of the extremes of the range of motion of the actuator and necessary limit stop compliance.